Certain strains of Escherichia coli carry plasmids which confer on the most bacterium the ability: 1) to produce an antibiotic-like protein, called colicin whose adsorption to specific bacterial receptors leads to cell death, and 2) to survive treatment with homologous colicin, called immunity. To further our understanding of colicin action, we are undertaking a program 1) to elucidate the mode of action of colicin Ia, 2) to isolate and characterize colicin Ia tolerant mutants, 3) to determine the mechanism of colicin Ia immunity, 4) to utilize the colicin Ia receptor to probe events in membrane biogenesis and 5) to initiate studies on the molecular biology of the I-plasmids. To gain insight into the molecular events occurring in membranes damaged by colicin Ia, we will study the effects of the colicin on transmembrane electrical and chemical gradients of whole cells. These experiments will be followed up by studies on model membranes. We expect to determine the molecular basis whereby colicin Ia tolerant mutants are defective in membrane energetics. Such studies may be useful in delineating components of cellular energy transduction. Using ferritin labeled anti-receptor antibody to allow electron microscopic visualization of the colicin Ia receptor, we intend to study several aspects of membrane biogenesis. Using our ability to control receptor integration into the bacterial outermembrane, we expect to be able to observe the early events of receptor insertion. We intend to determine the structural and genetic organization of the Col I plasmids. These studies will involve the construction of restriction maps and the isolation of plasmid mutants generated by insertion of translocation elements into these plasmids. Correlations between structural features and the positions of genetic loci will depend upon such methods as heteroduplex mapping and hybridization of specific plasmid messenger RNA species to particular restriction fragments.